Solid oxide fuel cell modules comprising a plurality of solid oxide fuel cells connected in electrical series are known.
In our European patent EP0668622A1 a solid oxide fuel cell module comprises a plurality of solid oxide fuel cells arranged on the flat surfaces of a hollow support member. The solid oxide fuel cells extend laterally across the full lateral extent of the surfaces of the hollow support member and the solid oxide fuel cells are spaced apart longitudinally on the surfaces of the hollow support member. The adjacent solid oxide fuel cells are connected electrically in series by an interconnector. Each interconnector extends laterally across the full lateral extent of the surface of the hollow support member to electrically connect an anode electrode of one solid oxide fuel cell with the cathode electrode of an adjacent solid oxide fuel cell.
The main parameters of the solid oxide fuel module are the fuel cell active length, the fuel cell pitch and the fuel cell gap. The fuel cell active length is the length of the solid oxide fuel cell longitudinally along the hollow support member. The fuel cell gap is the distance between adjacent solid oxide fuel cells. The fuel cell pitch is the sum of the fuel cell active length and the fuel cell gap.
The fuel cell active length and the fuel cell pitch are selected to optimise performance of the solid oxide fuel cell module. The fuel cell gap should be as small as possible to maximise the fuel cell length as a proportion of the fuel cell pitch. However, the fuel cell gap is dictated by the need for an interconnector to electrically connect the adjacent solid oxide fuel cells in series and to provide a space between the interconnector and the electrodes of the adjacent solid oxide fuel cells. The fuel cell gap may be reduced by reducing the length of the interconnector and the spaces. However, this makes it difficult to accurately align the interconnectors and the electrodes to avoid electrical failure of the fuel cell structure. Thus the minimum size of the fuel cell gap is restricted by this requirement and hence the fuel cell active length as a proportion of the fuel cell pitch is not maximised.